There is high demand for high-refractive-index, low-dispersion optical glasses as materials for optical elements such as various lenses. For example, such lenses can be combined with high-refractive-index, high-dispersion lenses to constitute compact, highly functional optical systems for the correction of chromatic aberration.
Employing an aspherical, optically functional surface in a high-refractive-index, low-dispersion lens makes it possible to obtain various optical systems of even greater functionality and compactness.
Precision press molding is known as a method of efficiently manufacturing optical elements of glass that are extremely time-consuming and costly to manufacture by processes such as grinding and polishing, such as aspherical lenses. A high-refractive-index, low-dispersion optical glass that is employed in precision press molding is disclosed in JP 2005-247613A (hereinafter referred to Patent Reference 1).
The object of Patent Reference 1 is to provide an optical glass, intended for the manufacturing of glass optical elements of high shape precision with high productivity, that has a high refractive index and low dispersion with a low glass transition temperature, and that softens at low temperatures permitting precision press molding. It discloses an optical glass comprised of essential components in the form of B2O3, La2O3, Gd2O3, and ZnO that has a refractive index (nd) exceeding 1.86, an Abbé number (vd) of less than 35, and a glass transition temperature (Tg) of 630° C. or lower.